AWS End User Message for OTP for two countries with Sender ID for the existing country

When expanding your AWS End User Messaging OTP service to include New Zealand, you may be able to use your existing setup with some modifications, but there are important considerations to keep in mind:

1. Sender ID compatibility: The Sender ID you're currently using for another country may not be automatically valid or optimal for use in New Zealand. Each country has its own regulations and requirements for Sender IDs.

2. Single region setup: You don't necessarily need to create an entirely separate setup in a different AWS region for New Zealand. You can potentially use a single region to send messages to multiple countries, as long as that region supports sending to your target countries.

3. Configuration adjustments: You'll need to update your existing configuration set to include rules for New Zealand. This can be done by modifying your account's default configuration to manage SMS settings for both countries from one place.

4. Protect configurations: Ensure your protect configuration includes rules that allow sending to New Zealand.

5. Compliance and best practices: Review the specific requirements and regulations for SMS messaging in New Zealand to ensure compliance with local laws and best practices.

The impact of using a Sender ID from a different country for messages to New Zealand could include:

1. Potential regulatory issues: New Zealand may have specific requirements for Sender IDs that your existing one doesn't meet.
2. Reduced trust: Recipients in New Zealand might be less likely to trust messages from an unfamiliar or foreign-looking Sender ID.
3. Possible delivery issues: Using an inappropriate Sender ID could potentially affect message deliverability.

To ensure optimal performance and compliance, it's recommended to:

1. Check if your existing Sender ID is suitable for use in New Zealand.
2. If not, consider registering a new Sender ID specifically for New Zealand if required.
3. Update your configuration set and protect configuration to include New Zealand.
4. Ensure you're using the E.164 number format for all phone numbers.

If you're unsure about the specific requirements or best approach, it's advisable to consult with AWS support to ensure you have the correct setup for sending OTPs to New Zealand.
Sources
AWS End User Messaging for 2 countries do I need two setups for different regions | AWS re:Post
How to Send SMS Using a Sender ID with AWS End User Messaging | AWS Messaging & Targeting Blog
SNS - Phone number | AWS re:Post

Please note that New Zealand does not support SenderID. AWS End User Messaging SMS highly recommends procuring a dedicated short code for all traffic being sent to New Zealand. Without a dedicated short code, AWS End User Messaging SMS still attempts to send messages to New Zealand recipients using a shared pool of short codes. Due to local carrier restrictions around shared numbers, deliverability over these shared numbers are made on a best-effort basis.

[+] https://docs.aws.amazon.com/sms-voice/latest/userguide/phone-numbers-sms-by-country.html#sms-support-note-6